What was found
DURING CLIMBOUT AT APPROXIMATELY 28,000 FEET, THE LEFT MAIN LANDING GEAR GREEN LIGHT ILLUMINATED. NO VIBRATION OR YAW WAS FELT. HYDRAULIC PUMP WAS SWITCHED TO HIGH WITH NO CHANGE. FLIGHT RETURNED TO DTW AND LANDED WITHOUT INCIDENT. LIGHT REMAINED ON THROUGHOUT GEAR EXTENSION WITH NO FLICKERING. MAINTENANCE FOUND LEFT MAIN GEAR GREEN LIGHT SOCKET SHORTING TO GROUND. REPLACED SOCKET AND OPERATIONAL CHECK NORMAL.